1. Field of the Invention
This invention relates primarily to a method and apparatus for controlling the automatic addition of detergent into a commercial warewashing machine. There are two key problems addressed by the invention. One is the detergent addition itself. The other is the determination of an appropriate concentration set-point. By making the detergent feed dependent upon the real-time concentration change rate, detergent overuse is reduced during the detergent addition. Adjusting detergent concentration set-points to correspond to changing account conditions also helps to maximize the performance of the warewashing process.
2. Description of Related Art
It is known in the art to provide warewashing machine systems with detergent controllers. Typically, such systems operate in an on-off mode, proportional mode or a combination thereof. The systems control the detergent concentration level to a pre-set detergent concentration level (set-point). The systems do not compensate for varying chemical injection rates and therefore exceed this set-point. They indirectly sense detergent concentration by measuring solution conductivity. The major perceived benefits of this type of controller is that the addition of, and concentration maintenance of, detergent to the warewashing machine is achieved without manual intervention.
However, these controllers do have some major shortcomings. The detergent concentration set-point consists of a single pre-set value for all wash cycles. Unless the set-point is manually reset, the wash items are subjected to the same concentrations of detergent in the wash solution, regardless of the meal period or type of soil present on the wash items. Therefore, to be certain of maintaining an acceptable cleaning result, the set-point is selected for a worst case condition. This results in detergent overuse. In addition, the detergent controllers feed detergent based on proportional control, reacting to the relationship between the setpoint and the current concentration. They do not compensate for the detergent feed rate which also causes detergent overuse or excessive wear on the feeder equipment.